It is well-known that the size-divergence product (SDP) of a light beam is an optical invariance throughout an optical system.
It is also well-known that the properties of light beam from edge emitting semiconductor laser, or diode laser, are quite different from other laser beams in that its SDP in lateral direction (X), the direction parallel to its PN junction or quantum well plane, and SDP in transverse directions (Y), the direction perpendicular to PN junction or quantum well plane, are quite different which causes substantial difficulties in diode laser applications where a uniform beam property is required, for example to focus the beam into a small round spot.
To overcome the difficulty caused by the inherent asymmetric property of edge emitting diode laser, techniques have been developed which successfully reformed the laser beam, such as U.S. Pat. Nos. 5,168,401, No. 5,592,333, No. 6,240,116 and No. 4,763,975. U.S. Pat. No. 5,592,333 employs roof reflectors with dihedral angles of 60° and 70.5°, but beam overlapping in lateral direction is an issue which prevents it from focusing into small spot. In our recent patent (U.S. Pat No. 8,767,304), array of roof reflector is employed for beam twisting wherein polarized beam splitter (PBS) is used to de-couple the twisted array of light beams.
This invention adds one more approach to the effort in beam twisting for edge emitting diode laser beam. It is very compact and reliable and the optical efficiency is very high. In addition, its damage threshold and optical spectrum are limited by material properties when integrated version is employed.